Arc extinguishing material



March'ZO, 1951 R. H. AMUNDsoN- ET A1.

ARC EXTINGUISHING MATERIAL Filed Aug.

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'arresters and the like.

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Patented Mar. 20, 1951 ARC EXTINGUISHING MATERIAL Roald H. Amundson and Henry V. Dryer, Milwaukee, Wis., assignors to McGraw Electric Company, a corporation of Delaware Application August 25, 1949, Serial No. 112,380

' vices in which .an arc may be generated `by excessively high currents or voltages, and more particularly to an arc extinguishing material .Con-

Jtained within said devices capable of evolving arc -exti-nguish'ing gases which smother the arc and thereby quickly and eiectively break the circuit. 'Many different types of composition have been suggested for use as arc extinguishing materials in high voltage fuses, circuit breakers, lightning One of the common arc :extinguishing materials in use today is boric acid, .which decomposes under the condition of the arc togenerate water vapor and to leave a deposit .of boron oxide. The water vapor which is generated serves as an arc extinguishing gas.

In `addition to boric acid, variousother arc @extinguishing materials have been used in the past. Typical among these are materials such as ber and the various synthetic resins such as phenolic condensation products and amino- -plast resins. A disadvantage of the latter type -`capable of generating a large volume of an essenjtially non-combustible gas Within a short time after the arc has been struck. In this manner, Athe line is opened quickly to prevent damage due to excessively high currents.

In addition, the material and its fused residue must be relatively non-conductive to prevent restriking of the arc by conduction through the fused compound. In addition, the arc extinguishing material must be relatively insoluble in Water `so that it will not be affected by mois- Further, a good arc extinguishing material should have the property of moldability without the use of major proportions of inert binders.

An object of the present invention is to provide electrical devices in which an are maybe generated by excessively high currents or voltages and means within the arcing area which are decomposable by the Aheat of the arc to generate large volumes of I essentially non-combustible gases capable of quickly extinguishing the arc.

Another object of the present invention is to f y,provide arc extinguishing material having the property of negligible electrical `conductivity in 5 Claims. (Cl. 20D-120) Y The present invention relates to electrical del when decomposed by the action of the arc, leaves only `a negligible amount of carbonaceous residue.

Another object of the present invention is to provide material which is relatively resistant to atmospheric conditions and which may be used in outdoor installations without being deleteriously alected by the atmosphere.

We have now found that arcs generated by excessively high currents or voltages may be coinpletely and eiectively extinguished where the arcing area is provided with an arc extinguishing material comprising dirnethylglyoxime. lThis compound has the following structural formula:

CH3-o- CH3 Dimethylglyoxime may be crystallized as colorless crystals from dilute alcohol. The crystals have a melting point of approximately 237 C. and are insoluble in water.

Dimethylglyoxime may be molded into any desired form by the simple application of pressure in a suitable die, but small amounts of binders may be added if desired. For example, from about l0 to 20% of plaster of Paris can be incorporated together with the dimethylglyoxime crystals when the same are placed in the forming die.

Under the inuence of an electric arc, dimethylglyoxime decomposes into large volumes of arc extinguishing gases which contain components such as carbon dioxide, nitrogen, and oxides of nitrogen, and which are essentially non-innammable so that they quickly and effectively extinguish the existing arc. In addition, this compound Shows practically negligible conductivity in its fused state, and, consequently, does not have 'a .tendency to permit restriking of the arc after it has once been extinguished.

The extinguishing action is also veryrapidthe circuit being cleared Within a half-cycle of the impressed frequency after the arc has been initiated.

A further .description of the present invention will be made in connection with the attached sheet of drawings which illustrates one preferred embodiment of the invention as applied to a high voltage fuse assembly. It will be lappreciated that the arc extinguishing material herein described is useful in other types of elec'- trical devices where arcs are encountered, for example, in lightning arrestars, circuit breakers. and in cable insulation.

On the drawing:

, Figure 1 is a fragmentary cross-sectional view Soi. .a highvoltage fuseassembly oontaininsa fusible link associated with the arc extinguishing material; and

Figure 2 is a View taken substantially along the line II-II of Figure 1.

As shown on the drawings:

Reference numeral I denotes in general a high voltage fuse assembly comprising an outer cylinder II which is preferably composed of a resinous material such as a phenol formaldehyde resin of the Bakelite type. A metallic ferrule I2 surrounds one end of the cylinder I I and is held thereon by means of pins I3 and I4 to complete the supporting structure for the replaceable face unit.

The replaceable unit includes an intermediate sleeve I5 which is freely movable within the interior of the outer cylinder II, and said sleeve I5 is threaded at one end into a tube I6 and seated against a collar I'I. The collar I'l is secured in the outer cylinder II by means of pins I8. The end portion IG is secured within the sleeve II by means of a cap 29 threaded onto the ferrule I2 and seated against an annular shoulder 30 of the endportion I6.

A fuse link button I 9 formed with a flange 'portion 20 isdisposed within the end portion I6 .with the flange portion 20 overlying the ends thereof. Secured to the button I9 is a strain Wire 2I and a fusible link 22. The opposite ends of the strain Wire ZI and of the fusible link 22 are secured to one end'of a rod 23. The opposite end of the rod 23 is held by means of a connector 24 to a tensioned conducting lead 25.

Around the fusible link 22 there is provided a collar 26 Which is suitably composed of heat and `arc resistant material. L

When the link 22 is broken by an excessively high current, an arc Will be struck between the end of the link button I9 and the retreating end of the rod 23 as it is pulled out of the assembly through the action of the tensioning force applied to the connector 24. To extinguish the resulting arc, and thus clear the circuit at the 'earliest possible time, there is provided an arc .extinguishing structure consisting of a series of molded hollow cylindrical blocks 21 of an arc extinguishing composition comprising dimethylglyoxime. The blocks 2l are disposed about a major portion of the rod 23 and, in effect, surround the path of the arc drawn between the button IS and the rod 23. A restraining collar 28', which may consist of ber, is provided at one end of the block assembly and is threaded into the intermediate sleeve I5.

When the fuse has blown, the fuse elements may be replaced by unscrewing cap 29, removing .the end portion I6 and the elements contained within the intermediate sleeve I5, and replacing lthe same with a new cartridge.

While the drawing illustrates the arc extinguishing material in the form of hollow cylindrical blocks, the arcing area may also be provided with a single hollow cylinder composed of rdimethylglyoxime either alone or with a binder, or the compound may be applied to the surface of another arc extinguishing material such as -ber or a phenolic resin. j As previously discussed," dimethylglyoxime has :ainegligible conductivity in its fused state. In

making conductivity tests, the compoundwas vfused and a pair of electrodes werel inserted into the fused mass. An alternating current of 240 volts was thereupon impressed and current read- 'ings taken by means of a milliammeter. Under -Jthese.con'dtiona'` the current through the fused 4 dimethylglyoxime was insufficient to cause a reading on an ordinary milliammeter.

The efcacy of the material as an arc extinguishing medium was determined by positioning two stationary electrodes with a fusible link between the electrodes and determining the length of material necessary to extinguish the arc created by the failure of the fuse under overload conditions. Thus, the usefulness of the material as an arc extinguishing medium is inversely proportional to the length of material necessary to extinguish the arc.

Under the test conditions mentioned above, a block of boric acid one and one-half inches in length was necessary before the arc was extinguished. Under the identical test conditions, a length of only one inch was required when using dimethylglyoxime as the arc extinguishing mate rial.

From the foregoing, it will be apparent that we have herein provided arc extinguishing material capable of completely and effectively extinguishing arcs-caused by current overloads in electrical systems. The material of the present in.- vention is non-conductive in its fused state so that there is no possibility of restriking the arc by conduction through the fused material after the arc has been initially extinguished. In addition, dimethylglyoxime is capable of being molded into a self-sustaining structure not affected by atmospheric conditions to any substantial degree.

Itwill be understood that modifications' and variations may be Veffected Without departing from the scope of the novel concepts of the present invention. 1

We claim as our invention:

l. In an electrical circuit including means for forming an arc, means along the path of the arfc capable of evolving an arc extinguishing gas comprising dimethylglyoxime. i

2. In an electrical circuit comprising means for forming an arc, and means along the path of the arc capable of evolving an arc extinguishing gas and comprising hollow cylindrical blocks of dimethylglyoxime.

3. In an electrical circuit comprising means for forming an arc, means along the path of the arc capable of evolving an arc extinguishing gas and comprising molded cylindrical blocks of dimethylglyoxime and a binder.

4. In a fuse assembly comprising a fusible link, an arc extinguishing material associated there- Withcapable of evolving an arc extinguishing gas in the presence of an arc and comprising dimethylglyoxime.

5. In a fuse assembly comprising a fusible link, an arc extinguishing material associated therewith capable of evolving an arc extinguishing material upon the failure of said link and comprising hollow cylindrical blocks of molded dimethylglyoxime. l v f f v ROALD H. AMUNDSONL HENRY V. DRYER.

iile of this patent:

UNrrEn STATESA Prflfrnrrrs .ifi

Number Name I ."Date y,

t 2,089,050 Burmeister Aug. 3, 1937 2,157,815 Boyer May 9, 1939 2,328,825 McMahon Sept. 7, 1943 DAlelio June 12, y194,5 

